1. Field of the Invention
The present invention pertains to a volumeter.
Devices of this type are suitable for measuring the volume of items with a surface which cannot be measured by simple geometric outlining and/or a surface which has individual structures such as straps, strings, layers of packaging paper, etc., or which is deformable. The device serves primarily but not exclusively to determine the volume of packages or similar items which are to be sent through the mail.
In addition, the invention pertains to a self-service postal station which is equipped with a volumeter of this type.
2. Description of the Related Art
Self-service postal stations of this type are known (see, for example, WO 92/17,861 and EP No. 643,374). At these postal stations, however, it is primarily the weight and not the volume of the postal item which is used to determine the amount of postage required. Only the maximum dimensions of the postal item are limited by mechanical devices (size of the feed slot). Additional light-optic sensors monitor the positioning of the postal item within the acceptance space and its required minimum dimensions. In another known system (Zuhlke Engineering AG, Schlieren-Zurich, Publication No. 66, "Developing New Products and Production Processes with Automation"), a linear light barrier determines the thickness of the item to be mailed (a letter), which is merely inserted into the receiving slot, and an electronic camera determines the surface area of the item. The volume of the letter is then calculated from these two values. To improve the measurement racy, a Fresnel lens is swung between the camera lens and the item being mailed so that the focal points of the camera lens and the Fresnel lens coincide. This solution is expensive, and the measured volume is also negatively affected by various features specific to the item being mailed (material projecting beyond the surface of the item such as flaps of packaging paper, strings, etc.).
The transport costs of an item, however, must often be determined not only on the basis of weight but also on the basis of the volume of the item. It has now been shown that, for a wide variety of reasons (cost, technical complexity, avoidance of damage to the item, etc.), volumes should be measured by means of contactless measuring methods (e.g., light-optic, ultrasonic sensors, etc.). In these measurement methods, however, the disadvantage is that a correct measurement can be disadvantageously affected by the structure and nature of the item. For example, projecting folds or edge reinforcing strips on items wrapped in packaging paper or loosely attached string can cast shadows and thus easily fool the device into concluding the item is larger than it really is. Items which rock back and forth or which fail to come to rest in some other way during the measurement are also measured incorrectly.